1. Field of the Invention
The present invention relates to a method of detecting microbiologically induced corrosion (M.I.C.) in industrial facilities, for example in the sphere of offshore structures: platforms, subsea pipes, wells, etc. Other spheres can also be concerned, such as the nuclear industry, harbour structures, geothermal facilities, the food-processing industry, among others.
2. Description of the Prior Art
The behavior of metal surfaces under working conditions can be followed by means of a programmer controlling the detector. According to the reaction of the detector towards the surrounding medium, a corrosive attack can be anticipated or detected, and facilities degradation can be anticipated.
In order to carry out a microbiologically induced corrosion experiment, it is necessary to have bacteria in a culture medium. The bacteria presently used belong to the Desulfovibrio gabonensis species (DSM 10636). The following document describes this bacterium: Desulfiovibrio gabonensis sp. Nov., “A New Moderately Halophilic Sulfate-Reducing Bacterium Isolated From An Oil Pipeline”, by Tardy-Jacquenod C., Magot M., Laigret F., Kaghad M., Patel B.K.C., Guezennec J., Matheron R., Caumette P. (1996) Int. J. Syst. Bacteriol. 46:710-715.
The strain has a maximum growth for a pH value ranging between 6.9 and 7.3, a temperature of 30° C. and a NaCl salinity of 5 to 6%. It is strictly anaerobic, reduces sulfate to sulfide (hence the abbreviation S.R.B., Sulfate-Reducing Bacterium), and the substrates that are oxidized by the anaerobic respiration of the sulfur compounds are, among others, lactate and ethanol.
The latter point explains the corrosive character of such bacteria. In fact, it is not the bacteria themselves that attack the steel, but rather their metabolic products that deteriorate the metal structures.
The process is then sustained by the development of the bacteria which gather together and form a biofilm, and the corrosion rates can reach such values that one centimeter of steel can be pierced in less than a year.